View Full Version : heat treating double edged blades

01-30-2003, 08:50 AM
I am going to harden a double edged blade for the first time and the only tool I've got to get the blade to critical is a gas forge. I'm wondering if I can get only the edges, and not the spine, up past critical for hardening. Will the spine be too soft without it too being hardened and then tempered like I usually do for single edged blades?

Neil Kessler

Jamey Saunders
01-30-2003, 09:01 AM
The way I understand you, you want to harden both edges, but leave the center soft. If I had to do this, I'd use a refractory clay like what is used in hardening Japanese swords. Even so, I'm pretty sure the center of the dagger would get pretty hard, but it will be drawn back in the temper process. I would suggest that you are going to be OK if you just heat to critical, quench, and temper.

Ray Rogers
01-30-2003, 09:53 AM
I agree with jsaund22. In theory you might be able to get the edges hard and keep the center soft by having the blade in the forge just the right amount of time and using the clay on it but who knows what that length of time would be? Too many variables.

Better to just heat , quench, and temper the whole blade. Then, if you have a fine tipped torch (and you think it's worth the trouble), keep the edges in water and draw the temper of the center with the torch ...........

01-30-2003, 06:31 PM
Okay. I think I didn't phrase my question clearly. Whenever I've heat treated single edge blades with a thick spine using a gas forge, it was fairly easy to just put the spine of the blade up to the mouth of the forge until it gained enough heat so that I could then start exposing the thin edge and have the thick spine and thin edge come up to critical at around the same time. Then, when I quench it all gets hardened, I can temper, then differentially temper the spine to blue, etc.

My trouble is that I can't really do that with a double edge blade (without using a torch to selectively heat the center before heating the edges). So, it's not that I WANT to not harden the center, it's that I can't get it over critical without overheating the edges (without using a torch) and what I'm wondering is: is a spine that isn't quenched and tempered to blue TOO soft?

Thanks again and sorry for not being more clear in my original post.


Jamey Saunders
01-30-2003, 09:25 PM
OK, now we're getting somewhere. I did misunderstand your first post.

I don't think you really have to worry about the center being too soft. Many makers heat their blades to critical and just quench the edge, leaving the back to cool naturally. They will then temper. This makes for a very soft spine, but it's tough and flexible. The same should be true for the center section of your dagger.

If you really do want to get the center up to critical, I would think that if you are careful, you can get everything up to that temperature by putting it into the forge until the edges are just short of being too hot, then removing it until the edge cools. The thin edges will cool faster than the thicker center, and when they do cool, you can re-insert the blade into the forge to continue heating. I would think that after several cycles of this, the whole blade will come up to a good temp. [DISCLAIMER] I have never done this. I do my HT in an electric oven.

Maybe someone else who heat treats daggers in a forge will give us both some pointers.

mike koller
01-30-2003, 09:39 PM
Cycling the blade back and forth like mentioned above will work to harden the whole blade, but you can just bring the edges up to non-magnetic and fully quench and get a differentialy HT blade.

With out seeing the blade,and it's size(width,thickness,etc...) it would be difficult to say if clay would do the same trick.

Remember not to stir the oil with the blade,it will cause warping and the thinner dagger will prolly be more likely to warp.

01-31-2003, 10:11 AM
Outstanding! This is just the info I needed and then some! Thanks for all your help.


01-31-2003, 03:47 PM
there's nothing bad or undesirable i can figure about havint a soft spine,especially on a dag,or double edge knife.For that type of knife that would be best,The edges would do it's job,while the spine absorbs the shock,very good